1、
Repeat v. No matter what happened in history, people tend to forget and then history repeats itself.
要紧趋向于做某事重复不管历史上发生过什么，人们往往会忘记，然后历史就会重演
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2、
The operations manual is beneficial in case major problems occur that require urgent changes.
当发生重大问题，需要紧急更改时，操作手册可以提供帮助。
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3、
In the past, there have been many endangered animals. Now they are extinct.
过去有很多濒危动物, 现在却灭绝了,这要紧吗?
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